Apparatus and method for thermal de-burring of slotted well liners

ABSTRACT

A method and apparatus for removing burrs from inside slotted metal liners exposes the burrs to a high-intensity gas flame that effectively oxidizes or incinerates the burrs, without inducing undesirable temperature levels in the parent metal of the slotted liner. This is accomplished using a torch head assembly having multiple gas torch nozzles disposed radially around the circumferential perimeter of the torch head, such that when the torch head is passed through the interior of a slotted liner, the flames are directed toward the interior surface of the liner. Auxiliary oxygen is introduced at the nozzle outlets, resulting in a large increase in flame velocity and intensity and, in turn, an increase in the flame temperature. The auxiliary oxygen may be introduced through annular passages surrounding the nozzles, such that the auxiliary oxygen effectively forms a cylindrical curtain surrounding the flame at each nozzle.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for removingburrs from internal surfaces of tubular goods, and in particular forremoving burrs from internal surfaces of slotted. pipe used as liners inoil and gas wells.

BACKGROUND OF THE INVENTION

In the production of oil or gas from an subsurface formation, steelliner pipes with multiple longitudinal slots (“slotted liners”) arecommonly installed in both vertical and horizontal wells to allow oil orgas present in the formation to enter the wells, whereupon the oil orgas can then be pumped or otherwise lifted to the surface forprocessing. The slots must be narrow enough to prevent significantamounts of formation materials from entering and clogging up the welland associated equipment such as pumps. For wells installed informations containing fine-grained materials, liner slot width may needto be as narrow as 0.04 inches (1.0 millimeter) or even considerablyless. The slots must be long enough and numerous enough to allow foreffective flow into the liner, without reducing the liner's structuralstrength below safe levels. The liner's structural strength (especiallyits flexural strength) is particularly important for horizontal wells,in which the liner must retain sufficient strength to be bent throughtransition sections between vertical and horizontal wellbores withoutfracture or excessive plastic deformation.

The slots may be of any convenient length, but they are typically in therange of 3 to 4 inches (75 to 100 millimeters) long. They are usuallyarrayed at uniform spacing about the circumference of the pipe, atradial intervals as low as 5 degrees. They are commonly cut into theliner sidewall using narrow circular slitting blades. One known methoduses a “gang mill” fitted with multiple slitting blades radiallyoriented on planes passing through the longitudinal axis of the liner.As the liner is moved longitudinally relative to the gang mill, theblades are deployed so as to cut slots of desired length through theliner sidewall.

Rather than making perfectly clean cuts, the slitting blades tend toleave jagged burrs or tendril-like “wickers” where the slots interceptthe interior surface of the liner. These burrs and wickers areundesirable for a variety of reasons, so the production of slottedliners typically includes steps to remove them, but known methods ofdoing so are not entirely satisfactory. One common method is to run adevice commonly called a “stinger” through the slotted liner. Thestinger has multiple rotating blades disposed such that they willessentially scrape the interior perimeter of the liner as the stingerpasses through. The intent is that the rotating blades will cut off thewickers, which can then be removed from the liner by compressed air orother means.

However, this method has proved to be only partially effective, becausethe scraping blades tend to bend the burrs and wickers and push themback across or into the slots, causing a direct reduction in the openslot area available for passage of oil into the liner. This problem isparticularly evident for slot widths of 0.04 inches (1 mm) and less. Theeffective slot area tends to become further reduced when the liner isplaced in service, because foreign materials entering the slots build upon the bent-back wickers, causing the slots to become partially ortotally plugged.

Other mechanical methods, such as honing or burnishing, have been usedin an attempt to polish the wickers down. However, these methods havesimilar drawbacks, in that they tend to simply brush some or all of thewicker metal back into the slots.

When using known de-burring methods having such significant drawbacks,it may be necessary to allow for slot plugging by providing a greateramount of slotting than might otherwise be required. It has beenobserved that slot plugging can reduce the effective permeability of aslotted liner by as much as 40% to 60%, so in order to obtain a desiredpermeability, liners may have to have a slotted area up to or more thantwice as large as the area theoretically required for a givenapplication. Such extra slotting obviously increases liner fabricationcost. It also decreases the structural strength of the liner, possiblyentailing the use of liners with greater wall thickness, thus increasingthe total cost of the slotted liner even further.

In addition to the foregoing problems, wickers or any other materialleft inside slotted liners can damage or interfere with expensivedown-hole tools used in well-servicing operations.

A possible alternative approach to wicker and burr removal would bethermal de-burring; i.e., exposing the wickers and burrs to ahigh-temperature flame. It is well known that burrs of steel or othermaterials can be burned off and effectively incinerated if subjected toa sufficiently hot flame. This would facilitate very effective removalof burrs from a slotted liner, as it would be fairly simple to removethe residue from the process (i.e., oxides) using compressed air,high-pressure water blasting, or other conventional means.

For the type of steel commonly used for slotted liners, effective use ofthis method would require heating the burrs to temperatures in the rangeof 6000° F. (3316° C.). At the same time, though, care would have to betaken to ensure that the temperature of the main body of the liner doesnot become excessive, in order to prevent undesirable metallurgicalchanges in the parent metal. This would not be overly difficult if thehigh-temperature flame could be effectively focused or concentrated onthe burrs and not on the main body of the liner, because the much largermass of the liner (i.e., compared to the mass of the burrs) would allowefficient dissipation of the heat applied to the burrs throughconduction, without excessive temperature build-up in the parentmaterial. However, it is virtually impossible to direct a flame towardburrs inside a steel liner without exposing the main body of the linerto the flame. Furthermore, the inventor has observed that whenconventional flame sources such as acetylene torches are used in anattempt to heat burrs inside a slotted liner to temperatures sufficientto achieve vaporization, the flame must dwell upon the burrs for so longthat excessive localized heating of the parent metal is unavoidable. Theprior art appears to disclose no solution to this problem.

For the foregoing reasons, there is a need for wicker-removal andde-burring apparatus and methods that can remove burrs and wickers fromslotted metal liners with substantially greater effectiveness than knownapparatus and methods. In particular, there is a need for such apparatusand methods that can remove burrs and wickers by exposure to anoxidizing flame, without raising the temperature of the adjacent parentmetal so high as to cause metallurgical changes or other undesirableeffects. The present invention is directed to these needs.

BRIEF SUMMARY OF THE INVENTION

In general terms, the present invention is a method and apparatuswhereby burrs inside a slotted metal liner may be exposed to a gas flamehot enough as to effectively oxidize or incinerate the burrs, withoutinducing undesirable temperature levels in the parent material. This isaccomplished by providing a torch head having multiple gas torch nozzlesdisposed around the circumferential perimeter of the torch head, suchthat when the torch head is passed through a slotted liner, the flamesare directed toward the interior surface of the liner. The apparatus isadapted to deliver a substantially stoichiometrically-balanced fuelmixture (i.e., a combustion gas and an oxidizing gas) to the nozzles, soas to produce substantially neutral-burning flames at the nozzles. Ithas been determined, through testing, that the temperature of aneutral-burning flame will increase considerably in the presence ofoxygen. In accordance with the present invention, therefore, provisionis made for introducing an auxiliary oxidizing gas—preferably pureoxygen—near the nozzle outlets, thus increasing the flame velocity andintensity, and in turn causing a significant increase in flametemperature.

The temperature of the torch flames produced according to the presentinvention is thus considerably higher than it would be without theintroduction of auxiliary oxidizing gas. It has been found that when thetorch head, having a suitable number of nozzles and having auxiliaryoxidizing gas introduced around the torch flames, is passed through aslotted liner at an appropriate rate of travel, the flame intensity issufficient to incinerate a high percentage of burrs and wickers from theliner, without excessive temperature rise in the parent metal. Theappropriate torch head travel speed will depend on a variety of factors,including liner diameter and wall thickness, feed pressures of the fuelmixture components and the auxiliary oxygen, the number of nozzles onthe torch head, and the distance from the nozzle outlets to the innersurface of the liner.

Accordingly, in one aspect the present invention is a de-burringapparatus, for removing burrs from interior surfaces of a slotted metalliner, said apparatus comprising:

-   -   (a) a torch carrier body having a front end and a rear end;    -   (b) a torch head connected to the torch carrier body at the        front end thereof, said torch head having a longitudinal axis        and a circumferential lateral surface, said torch head having        formed therewithin:        -   b.1 a fuel plenum, for receiving a fuel mixture comprising a            combustion gas and a primary oxidizing gas;        -   b.2 an auxiliary plenum, for receiving and conveying an            auxiliary oxidizing gas from a source of auxiliary oxidizing            gas;        -   b.3 a plurality of fuel channels, each fuel channel having            an outer end and an inner end, and each fuel channel at its            inner end being in fluid communication with the fuel plenum;            and        -   b.4 a plurality of nozzle ports, each nozzle port extending            inward from the circumferential lateral surface of the torch            head and having an inner wall surface, and each nozzle port            being in fluid communication with a corresponding one of the            fuel channels; and    -   (c) a plurality of torch nozzles, each nozzle having an outer        end, an inner end, and a side surface, an inner end, and each        nozzle having a fuel passage extending through the nozzle        between said inner and outer ends;        said apparatus being characterized by:    -   (d) each nozzle being retainingly installed within a        corresponding nozzle port and defining an interstitial space        between the side surface of the nozzle and the inner wall        surface of the nozzle port, said interstitial space having an        outer end in proximity to the outer end of the nozzle;    -   (e) the outer end of each nozzle extending close to or beyond        the circumferential surface of the torch head;    -   (f) the inner end of each nozzle being sealingly engaged with        the fuel channel associated with the corresponding nozzle port,        such that the outer end of the fuel passage of each nozzle is in        fluid communication with the fuel plenum; and    -   (g) each interstitial space being in fluid communication with        the auxiliary plenum, and intercepting the circumferential        surface of the torch head, such that auxiliary oxidizing gas can        flow from the auxiliary plenum into the interstitial spaces and        exit at the outer end thereof.

In another aspect, the invention is a method of removing burrs frominterior surfaces of a slotted metal liner, said method comprising thesteps of:

-   -   (a) introducing a fuel mixture comprising a combustion gas and a        primary oxidizing gas into the fuel plenum of the torch head of        a de-burring apparatus substantially as described immediately        above, such that the fuel mixture flows into the fuel passages        of the torch nozzles of the torch head;    -   (b) igniting the fuel mixture exiting the fuel passages of the        torch nozzles to create torch flames;    -   (c) introducing an auxiliary oxidizing gas into the auxiliary        plenum of the torch head, such that the auxiliary oxidizing gas        flows out of the interstitial spaces around the torch nozzles;    -   (d) regulating the respective flowing pressures of the fuel        mixture and auxiliary oxidizing gas so that the torch flames are        of a temperature sufficient to substantially incinerate metal        burrs present on the interior surface of the slotted liner; and    -   (e) passing the torch head through the slotted liner at an        appropriate speed such that the torch flames are directed toward        the interior surface of the slotted liner so as to substantially        incinerate the metal burrs.

In a further aspect, the invention is a method of removing burrs frominterior surfaces of a slotted metal liner, said method comprising thesteps of:

-   -   (a) providing a torch head having one or more torch nozzles;    -   (b) delivering a fuel mixture comprising a combustion gas and a        primary oxidizing gas to the one or more torch nozzles;    -   (c) igniting the fuel mixture exiting the one or more torch        nozzles, thus creating one or more torch flames;    -   (d) introducing an auxiliary oxidizing gas in the immediate        vicinity of each torch flame so as to raise the flame        temperature to a level sufficient to substantially incinerate        metal burrs present on the interior surface of the slotted        liner; and    -   (e) passing the torch head through the slotted liner at an        appropriate speed such that the torch flames are directed toward        the interior surface of the slotted liner so as to substantially        incinerate the metal burrs.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying figures, in which numerical references denote like parts,and in which:

FIG. 1 is a perspective view of a typical slotted liner for use in oilor gas wells.

FIG. 2 is a perspective view of the torch head and torch carrier body ofa first embodiment of the apparatus.

FIG. 3 is a cross-sectional side view of the torch head and torchcarrier body of a second embodiment of the apparatus.

FIG. 4 a is a perspective view showing the torch head, flame shield, andcentralizer means of one embodiment of the apparatus.

FIG. 4 b is a cross-sectional perspective view of the torch head, flameshield, and centralizer means illustrated in FIG. 4 a.

FIG. 5 is a cross-sectional view of the torch head of an embodiment ofthe invention in which the torch nozzles are oriented substantiallyperpendicularly relative to the axis of the torch head.

FIG. 6 is a cross-sectional view of the torch head of an embodiment ofthe invention in which the torch nozzles are oriented with a forwardcant.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a slotted liner 100 of the general type that may bede-burred using the present invention may be used. The slots 102 in theslotted liner 100 shown in FIG. 1 are oriented parallel to thelongitudinal axis of the liner 100, but in other variations of slottedliner 100 the slots 102 may be oriented transversely or obliquelyrelative to the axis of the liner 100. However, the functioning of thepresent invention is not dependent upon or affected in any substantialway by the orientation of the slots 102 in the liner 100 beingde-burred.

As illustrated in the Figures, the de-burring apparatus 10 of thepresent invention includes a torch carrier body 12 having a front end 14and a rear end 16. The torch carrier body 12 is adapted to accommodateconduits 18 a, 18 b, and 18 c for conveying, respectively, a combustiongas, a primary oxidizing gas, and an auxiliary oxidizing gas fromrespective sources. Where the same type of gas is used for both theprimary and auxiliary oxidizing gases, a common source may be used. Atorch head 20, having a longitudinal axis A and a circumferentiallateral surface 22, is connected to the torch carrier body 12 at thefront end 14 thereof. The torch head 20 has multiple gas torch nozzles50 disposed (preferably, but not necessarily, at uniform spacing) aroundthe circumferential lateral surface 22 of the torch head 20, such thatwhen the torch head 20 is passed through the interior of a slotted liner100, flames from the torch nozzles 50 will be directed toward theinterior surface of the liner 100 and, therefore, toward any burrs orwickers that may be present in the vicinity of the slots 102 in theliner 100.

As particularly illustrated in FIGS. 5 and 6, the torch head 20 isformed so as to define a fuel plenum 30 for receiving a fuel mixturecomprising a combustion gas and a primary oxidizing gas. The fuel plenum30 may receive combustion gas and oxidizing gas conduits 18 a and 18 b,with these gases being combined within the fuel plenum 30, or thecombustion gas and oxidizing gas may be combined in a separate mixingchamber (not shown) and then delivered to the fuel plenum 30.

In addition, the torch head 20 defines an auxiliary plenum 32, which isin fluid communication with the auxiliary oxidizing gas conduit 18 c, asillustrated in FIG. 6. In the particular embodiment illustrated in FIG.6, the auxiliary oxidizing gas conduit 18 c, although not fully shown,passes through the fuel plenum 30 and discharges auxiliary oxidizing gasinto the auxiliary plenum 32 at point X.

The torch head 20 also defines a plurality of fuel channels 34, each ofwhich has an outer end 34 a, plus an inner end which is in fluidcommunication with the fuel plenum 30. Each fuel channel 34 is in fluidcommunication with a corresponding nozzle port 40 formed in the torchhead 20. Each nozzle port 40 intercepts the circumferential lateralsurface 22 of the torch head 20 and having an inner wall surface 42(which will typically, but not necessarily, be cylindrical). Each nozzleport 40 is adapted to receive and retain a torch nozzle 50, withclearance space between the nozzle 50 and the inner wall surface (orsurfaces) 42 of the nozzle port 40. Each nozzle 50 has a side surface 52(typically cylindrical), an inner end 50 a, and an outer end 50 b, plusa fuel passage extending through the nozzle 50 from inner end 50 a toouter end 50 b. The length of the nozzles 50 is selected such that theouter ends 50 a thereof will extend close to or beyond thecircumferential surface 22 of the torch head 20 when the nozzles 50 areinstalled in their corresponding nozzle ports 40. Accordingly, when anozzle 50 is installed in its corresponding nozzle port 40, with itsinner end 50 a in sealing engagement with the corresponding fuel channel34, a fuel mixture can flow from the fuel plenum 30 into the fuelchannel 34 and into fuel passage 54 of the nozzle 50, exiting therefromat the outer end 50 b of the nozzle 50, at which point the fuel mixturemay be ignited to create a torch flame.

The nozzles 50 may be of any suitable construction having centrallongitudinal fuel passages 54 for conveying the fuel mixture from a fuelplenum 30. In one embodiment, the nozzles 50 are conventional “MIGtips”; i.e., wire-feeder tips of a type commonly used in the metal-inertgas welding process. It has been found that acceleration of the fuelmixture as it exits the fuel passages 54 of the nozzles 50 facilitatesestablishment of a stable, neutral flame, by inducing a certain amountof backpressure and increasing the flame velocity. Accordingly, in oneembodiment of the apparatus of the invention, the fuel passages 54 ofthe nozzles 50 have a narrowing or constriction near the external endsthereof, so as to accelerate the fuel mixture as it exits the nozzles50.

The installation of a nozzle 50 into a corresponding nozzle port 40 willresult in the formation of an interstitial space 44 between the sidesurface 52 nozzle 50 and the inner wall surface (or surfaces) 42 of thenozzle port 40. The interstitial space 44 will have an outer end 45 inproximity to the outer end 50 a of the nozzle 50. The nozzle 50 willtypically be of cylindrical cross-section, and as previously mentioned,the nozzle port 40 will typically have a cylindrical inner wall surface42, so the interstitial space 44 will typically and preferably be ofannular cross-section. However, this characteristic is not essential tothe present invention. What is essential is that the interstitial space44 intercepts or is otherwise in fluid communication with the auxiliaryplenum 32, such that auxiliary oxidizing gas can flow from the auxiliaryplenum 32 into the interstitial space 44, and will exit from the outerend 45 thereof. Regardless, though, of the dimensional characteristicsof the interstitial space 44 at other points along its length, it willbe preferable for the exit width W of the interstitial space 44 (i.e.,at its outer end 45) to be substantially uniform, for reasons explainedbelow.

It can be readily seen that when a fuel mixture exiting from the fuelpassage 54 of the nozzle 50 has been ignited to create a torch flame,the auxiliary oxidizing gas exiting the interstitial space 44 willeffectively create a curtain or shroud of auxiliary oxidizing gassubstantially enveloping the torch flame. This flow of auxiliaryoxidizing gas in the vicinity of the torch flame substantially increasesflame velocity, intensity, and temperature. As mentioned, it ispreferable for the exit width W of the interstitial space 44 to beuniform, thus promoting uniform flow of auxiliary oxygen around theflame and correspondingly uniform resultant effects on the flame.

The nozzle ports 40 may be configured such that the axes of the torchnozzles 50 intersect the longitudinal axis A of the torch head 20 (i.e.,in radial fashion), and also at right angles to axis A, as may be seenin FIG. 5. It has been observed, however, that torch flame effectivenessmay be enhanced by tilting the flames forward. This has the beneficialeffect of increasing the temperature of portions of the liner 100immediately ahead of the torch head 20, thus decreasing the amount ofheat that needs to be transferred to the burrs and wickers when thetorch flames come into direct contact with them. The tilt of the flamesalso induces a forward-moving pressure wave inside the liner 100 thatassists in blowing debris from incinerated burrs and wickers out of theliner 100.

Accordingly, in the preferred embodiment of the apparatus, one or moreof the torch nozzles 50 (and their corresponding nozzle ports 40) have aforward cant, so that the flames from these nozzles 50 will be directedboth radially outward and toward the front of the torch head 20, asillustrated in FIGS. 3, 4 b, and 6. The forward cant angle may beselected to suit particular applications. By way of example, FIGS. 4 band 6 illustrate a 15° forward cant. However, beneficial results havealso been obtained using cant angles of 30°, 45°, and 60°, in torchheads 20 for use with liners having of nominal diameters of 3.5″, 4.5″,and 5.5″ (89 mm, 114 mm, and 140 mm) respectively.

It is not essential for the torch nozzles 50 to be installed in a radialconfiguration relative to the longitudinal axis A of the torch head 20.In one alternative embodiment (not shown), one or more of the nozzleaxes are oriented at oblique angles to axis A, such that the torchflames exit the torch head 20 in “pinwheel” fashion, thus creating aswirling effect to the flames as the torch head 20 moves through theliner 100. In a variation of this alternative embodiment, one or morenozzles 50 have a forward cant as well as an oblique orientationrelative to axis A.

The combustion gas may be any combustible gas having suitableheat-producing characteristics, and acetylene is one example. However,particularly beneficial results have been observed when using a mixtureof MAPP gas (i.e., methylacetylene-propadiene) and oxygen. Whileacetylene produces a higher flame temperature, it has been found that aMAPP gas flame is more stable than an acetylene flame. Propane ornatural gas, which also produce suitably stable flames, could also beused, but their heating values are lower than for MAPP gas, making thelatter more desirable to optimize burr removal rates. The fuel mixturepreferably will be substantially stoichiometrically balanced, so as toproduce substantially neutral-burning flames.

The auxiliary oxidizing gas may comprise air. However, particularlybeneficial results have been achieved using substantially pure oxygen asthe auxiliary oxidizing gas.

As previously mentioned, it has been found that when a torch head 20 inaccordance with the present invention, having a suitable number ofnozzles 50, is passed through a slotted liner 100 at an appropriate rateof travel, the flame intensity is sufficient to incinerate a highpercentage of burrs and wickers from the interior of the liner 100,without excessive temperature rise in the parent metal. The appropriatetorch head travel speed will depend on a variety of factors, includingliner diameter and wall thickness, feed pressures of the fuel mixturecomponents and the auxiliary oxygen, the number of nozzles 50 on thetorch head 20, and the distance from the nozzle outlets to the innersurface of the liner 100.

As only one representative example, it has been found that a travelspeed in the range of 4.0 to 4.5 feet (1.2 to 1.4 meters) per minute iseffective for de-burring a nominal 7-inch diameter steel liner (i.e.,7.75″ or 197 mm outer diameter; and 6.35″ or 161 mm inner diameter)using a torch head 20 having 48 radially-disposed nozzles 50 burning aMAPP gas mixture fed at approximately 20 pounds per square inch (138kiloPascals), with auxiliary oxygen fed at approximately 50 psi (345kPa), and with the radial distance between the nozzle outlets and theinner cylindrical surface 104 of the liner 100 being approximately 0.5inches (13 mm).

The apparatus 10 of the invention preferably includes fuel mixturecontrol means and auxiliary oxidizing gas control means, for regulatingthe flowing pressure of the fuel mixture and the oxidizing gasrespectively. It will be readily appreciated by persons skilled in theart that various known means for controlling or regulating the pressureof a flowing gas may be easily adapted for use as the fuel mixturecontrol means and auxiliary oxidizing gas control means.

In the preferred embodiment, the torch head 20 will also have a flameshield 70, which may be provided in the form of a collar or flangemounted rearward of the nozzles 50 and extending radially outward fromthe torch head 20, but stopping just short of the inner surface 104 ofthe liner 100 such that it does not impede passage of the torch head 20through the liner 100. The flame shield 70 serves two primary functions,the first of which is to shield from the flames those portions of theliner 100 which the torch head 20 has already passed by, thus furtherminimizing the temperature increase in the parent metal of the liner100. The second function or effect of the flame shield 70 is toconcentrate the torch flames in a region immediately adjacent to thenozzles 50, by preventing the flames from deflecting back over theregion previously exposed to the flames, thus optimizing heat transferto the burrs present inside the liner 100.

In the preferred embodiment, the apparatus 10 of the invention willinclude centralizer means 60, for ensuring that the longitudinal axis Aof the torch head 20 is substantially aligned with the axis of the liner100 through which the torch head 20 passes when the apparatus is in use,thus ensuring that all of the nozzles 50 are approximately equidistantfrom the inner surface 104 of the liner 100, so as to facilitatesubstantially consistent heat transfer from the nozzles 50 to the liner100 and any burrs or wickers present at or near the inner surface 104 ofthe liner 100. As particularly illustrated in FIGS. 4 a and 4 b, thecentralizer means 60 may include a plurality of rub bars 62 disposedradially about the perimeter of the torch carrier body 12, each rub bar62 being mounted to a bracket 64 hingingly connected to the of the torchcarrier body 12, and each bracket 64 having biasing means (such as aspring) for urging the rub bars 62 radially outward so as to rideagainst the inner surface 104 of the liner 100 as the torch head 20passes through. Other effective centralizing means will be readilyapparent to persons skilled in the art of the invention. For example,the rub bars may include (or be replaced by) rollers that will rollagainst the inner surface 104 of the liner 100.

Just as the liner 100 needs to be protected from excessive heatbuild-up, the temperature of the torch head 20 also should be keptwithin an acceptable range, to prevent metallurgical changes or otherundesirable effects. Accordingly, in the preferred embodiment, theapparatus 10 of the invention include torch head cooling means. Althoughthe torch head 20 may be effectively cooled using a gaseous coolant suchas air, in the preferred embodiment the torch head 20 is cooled bycirculation of a liquid coolant (which could comprise water or ethyleneglycol) through one or more coolant circulation chambers 24 formedwithin the torch head 20, analogous in principle to the coolantcirculation chambers in a liquid-cooled automotive engine. The coolantcirculation chambers 24 for the preferred embodiment of the inventionmay be located and configured within the torch head 20 in any convenientfashion, in accordance with principles and methods well known in theart.

In the preferred embodiment, the torch head 20 is fabricated at least inpart from steel. In an alternative embodiment, the torch head 20 isfabricated at least in part from a metal (such as titanium) that canwithstand higher temperatures than steel without undesirablemetallurgical or other effects, thus reducing the cooling load on thetorch head cooling means, or even eliminating the need or desirabilityfor torch head cooling means.

The torch head 20 may be fabricated in a number of sections that aresubsequently assembled by bolting or other suitable means. One exampleof this method of fabricating and assembling the torch head 20 isillustrated in FIG. 4 b; however, other arrangements may be possible.Individual sections of the torch head 20 may be machined from solidstock, or may be made as castings for machining as necessary to fashionrequired structural features. Casting methods may also be availablewhich enable the entire torch head 20 to be a single casting, to bemachined as necessary.

In the preferred embodiment of apparatus and method of the invention,the torch head 20 is movable through the liner 100 being de-burred. Inalternative embodiments, however, the liner 100 may be moved over astationary torch head 20. Suitable motive means for moving the torchhead 20 through the liner 100, or for moving the liner 100 over astationary torch head 20, will be readily devisable by persons skilledin the art. The motive means may include a extension member attached tothe rear end 16 of the torch carrier body 12, or integral with the torchcarrier body 12, and of a suitable length to facilitate insertion of thetorch head 20 into the liner 100 for substantially its full length. Inone embodiment of the apparatus, the motive means includes a pullrod/cable assembly connected to a hydraulic motor, for inserting thetorch head 20 into the liner 100 and retracting it therefrom. Othertypes of motors and components may be used for the motive means withoutdeparting from the present invention.

Preferably, the motive means includes torch head speed control means forregulating the rate at which the torch head 20 travels through the liner100. As will be appreciated by persons skilled in the art of theinvention, suitable speed control means may be readily provided by useor adaptation of known technology. To provide one example, torch headspeed control may be provided by use of a variable-speed motor as acomponent of the motive means.

It has been observed that the temperature at the outer surface of theliner 100 in the vicinity of the zone being exposed to the torch flamescan be a good indicator of the flames' effectiveness in removing burrsand wickers for a given torch head speed; i.e., whether the burrs andwickers are being exposed to the flames long enough for removal. Forexample, in one tested assembly, a measured liner temperature of about250° F. (121° C.) would indicate that the torch head speed was too fast,and that burr removal was less than optimally effective. This would inturn indicate that the torch head speed should be increased. At theother end of the scale, a measured liner temperature of about 350° F.(177° C.) would indicate that the torch head speed was too high. Theseapproximate temperature limits, for purposes of monitoring flameeffectiveness and for regulating torch head speed, may differ dependingon various factors including the number of torch nozzles, linerdimensions, and torch flame characteristics.

In view of the foregoing observations, the preferred embodiment of theapparatus of the present invention includes means for monitoring thetemperature of the parent metal of liner 100 in the general vicinity ofthe torch nozzles 50 as they pass through the liner 100. In aparticularly preferred embodiment, the temperature-monitoring means iscoupled to the motive means, using suitable known control technology,such that the torch head travel speed is automatically regulated inresponse to detected variations in parent metal temperature. As well asproviding an indication of torch flame effectiveness as discussed above,the temperature-monitoring means may also be advantageous to alert theoperator of the apparatus in the event that the parent metal temperatureapproaches or exceeds a selected maximum value above which undesirableeffects could result, in which case appropriate remedial or preventivesteps can be initiated.

When the torch head 20 is moving through the slotted liner 100 at anappropriate speed, the temperature rise in the parent metal of the liner100 should not to temperatures high enough to cause undesirablemetallurgical or other effects. However, it has been observed that theparent metal temperature tends to be higher at the crown of the liner100 than at lower locations, and this can result in longitudinal bowingof the liner 100 as it cools down. To mitigate or prevent thisundesirable condition, the preferred embodiment of the method of theinvention includes the additional step of rotating the liner relative tothe torch head 20, thus promoting uniform temperature rise in the parentmetal around the circumference of the liner 100. As a result, the liner100 will cool more uniformly and will therefore be less prone tolongitudinal distortion. Suitable means for rotating the liner 100 willbe readily apparent to persons skilled in the art, including but notlimited to the use of suitably shaped rollers to cradle the liner 100,with one or more of the rollers being a drive roller that can beactuated to rotate the liner 100.

It will be readily appreciated by those skilled in the art that variousmodifications of the present invention may be devised without departingfrom the essential concept of the invention, and all such modificationsare intended to be included in the scope of the claims appended hereto.

In this patent document, the word “comprising” is used in itsnon-limiting sense to mean that items following that word are included,but items not specifically mentioned are not excluded. A reference to anelement by the indefinite article “a” does not exclude the possibilitythat more than one of the element is present, unless the context clearlyrequires that there be only one such element.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A de-burring apparatus, for removing burrs from interior surfaces ofa slotted metal liner, said apparatus comprising: (a) a torch carrierbody having a front end and a rear end; (b) a torch head connected tothe torch carrier body at the front end thereof, said torch head havinga longitudinal axis and a circumferential lateral surface, said torchhead having formed therewithin: b.1 a fuel plenum, for receiving a fuelmixture comprising a combustion gas and a primary oxidizing gas; b.2 anauxiliary plenum, for receiving and conveying an auxiliary oxidizing gasfrom a source of auxiliary oxidizing gas; b.3 a plurality of fuelchannels, each fuel channel having an outer end and an inner end, andeach fuel channel at its inner end being in fluid communication with thefuel plenum; and b.4 a plurality of nozzle ports, each nozzle portextending inward from the circumferential lateral surface of the torchhead and having an inner wall surface, and each nozzle port being influid communication with a corresponding one of the fuel channels; and(c) a plurality of torch nozzles, each nozzle having an outer end, aninner end, and a side surface, an inner end, and each nozzle having afuel passage extending through the nozzle between said inner and outerends; said apparatus being characterized by: (d) each nozzle beingretainingly installed within a corresponding nozzle port and defining aninterstitial space between the side surface of the nozzle and the innerwall surface of the nozzle port, said interstitial space having an outerend in proximity to the outer end of the nozzle; (e) the outer end ofeach nozzle extending close to or beyond the circumferential surface ofthe torch head; (f) the inner end of each nozzle being sealingly engagedwith the fuel channel associated with the corresponding nozzle port,such that the outer end of the fuel passage of each nozzle is in fluidcommunication with the fuel plenum; and (g) each interstitial spacebeing in fluid communication with the auxiliary plenum, and interceptingthe circumferential surface of the torch head, such that auxiliaryoxidizing gas can flow from the auxiliary plenum into the interstitialspaces and exit at the outer end thereof.
 2. The de-burring apparatus ofclaim 1, further comprising centralizer means, for substantiallyaligning the longitudinal axis of the torch head with the longitudinalaxis of the slotted liner.
 3. The de-burring apparatus of claim 2wherein the centralizer means comprises a plurality of rub bars disposedcircumferentially around the torch carrier body, each rub bar beingrotatably mounted to a bracket hingingly mounted to the torch carrierbody, and each bracket having biasing means for urging the associatedrub bar radially outward.
 4. The de-burring apparatus of claim 1,further comprising a flame shield rearward of the nozzles.
 5. Thede-burring apparatus of claim 1, further comprising means for regulatingthe pressure of a fuel mixture flowing to the nozzles.
 6. The de-burringapparatus of claim 1, further comprising means for regulating thepressure of an auxiliary oxidizing gas flowing to the interstitialspaces.
 7. The de-burring apparatus of claim 1, further comprising torchhead cooling means.
 8. The de-burring apparatus of claim 7 wherein thetorch head defines one or more coolant circulation chambers forreceiving a circulating coolant fluid.
 9. The de-burring apparatus ofclaim 1 wherein the nozzle ports are substantially uniformly spacedcircumferentially around the torch head.
 10. The de-burring apparatus ofclaim 1 wherein at least one torch nozzle is radially oriented relativeto the longitudinal axis of the torch head.
 11. The de-burring apparatusof claim 1 wherein at least one torch nozzle is oriented substantiallyperpendicularly to the longitudinal axis of the torch head.
 12. Thede-burring apparatus of claim 1 wherein at least one nozzle is cantedtoward the front end of the torch head.
 13. The de-burring apparatus ofclaim 1 wherein at least one torch nozzle is oriented obliquely relativeto the longitudinal axis of the torch head.
 14. The de-burring apparatusof claim 1 wherein the fuel passage of at least one nozzle has aconstriction so as to accelerate a fuel mixture exiting therefrom. 15.The de-burring apparatus of claim 1 wherein at least one torch nozzle isa MIG tip.
 16. The de-burring apparatus of claim 1 wherein at least aportion of the interstitial space is of annular cross-section.
 17. Thede-burring apparatus of claim 1, further comprising motive means formoving the torch head relative to the slotted liner.
 18. The de-burringapparatus of claim 17 wherein the motive means is adapted to hold theslotted liner longitudinally stationary and move the torch head throughthe slotted liner.
 19. The de-burring apparatus of claim 17 wherein themotive means is adapted to hold the torch head longitudinally stationaryand move the slotted liner over the torch head.
 20. The de-burringapparatus of claim 17, further comprising torch head speed controlmeans, for controlling the torch head's rate of travel relative to theslotted liner.
 21. The de-burring apparatus of claim 1, furthercomprising temperature-monitoring means, for monitoring the temperatureof the slotted liner in the vicinity of the nozzles.
 22. The de-burringapparatus of claim 20, further comprising temperature-monitoring means,for monitoring the temperature of the slotted liner in the vicinity ofthe nozzles, and wherein the torch head speed control means is adaptedto adjust the torch head speed according to variations in linertemperature as measured by the temperature-monitoring means.
 23. Amethod of removing burrs from interior surfaces of a slotted metalliner, said method comprising the steps of: (a) providing a torch headhaving one or more torch nozzles; (b) delivering a fuel mixturecomprising a combustion gas and a primary oxidizing gas to the one ormore torch nozzles; (c) igniting the fuel mixture exiting the one ormore torch nozzles, thus creating one or more torch flames; (d)introducing an auxiliary oxidizing gas in the immediate vicinity of eachtorch flame so as to raise the flame temperature to a level sufficientto substantially incinerate metal burrs present on the interior surfaceof the slotted liner; and (e) passing the torch head through the slottedliner at an appropriate speed such that the torch flames are directedtoward the interior surface of the slotted liner so as to substantiallyincinerate the metal burrs, while simultaneously rotating the linerrelative to the torch head.
 24. A method of removing burrs from interiorsurfaces of a slotted metal liner, said method comprising the steps of:(a) introducing a fuel mixture comprising a combustion gas and a primaryoxidizing gas into the fuel plenum of the torch head of a de-burringapparatus according to claim 1, such that the fuel mixture flows intothe fuel passages of the torch nozzles of the torch head; (b) ignitingthe fuel mixture exiting the fuel passages of the torch nozzles tocreate torch flames; (c) introducing an auxiliary oxidizing gas into theauxiliary plenum of the torch head, such that the auxiliary oxidizinggas flows out of the interstitial spaces around the torch nozzles; (d)regulating the respective flowing pressures of the fuel mixture andauxiliary oxidizing gas so that the torch flames are of a temperaturesufficient to substantially incinerate metal burrs present on theinterior surface of the slotted liner; and (e) passing the torch headthrough the slotted liner at an appropriate speed such that the torchflames are directed toward the interior surface of the slotted liner soas to substantially incinerate the metal burrs.
 25. The de-burringmethod of claim 24 wherein the step of passing the torch head throughthe slotted liner is effected by holding the liner longitudinallystationary and moving the torch head through the liner.
 26. Thede-burring method of claim 24 wherein the step of passing the torch headthrough the slotted liner is effected by holding the torch headstationary and passing the liner over the torch head.
 27. The de-burringmethod of claim 24 further comprising the step of rotating the linerrelative to the torch head.
 28. The de-burring method of claim 24wherein the torch head defines one or more coolant circulation chambers,and further comprising the step of circulating a coolant fluid throughthe coolant circulation chambers.
 29. The de-burring method of claim 28wherein the coolant fluid is a liquid coolant.
 30. The de-burring methodof claim 29 wherein the liquid coolant comprises water.
 31. Thede-burring method of claim 29 wherein the liquid coolant comprisesethylene glycol.
 32. The de-burring method of claim 28 wherein thecoolant fluid comprises a coolant gas.
 33. The de-burring method ofclaim 32 wherein the coolant gas comprises air.
 34. The de-burringmethod of claim 24 wherein the combustion gas is selected from the groupconsisting of MAPP gas, acetylene, propane, and natural gas.
 35. Thede-burring method of claim 24 wherein the fuel mixture is substantiallystoichiometrically balanced.
 36. The de-burring method of claim 24wherein the primary oxidizing gas comprises substantially pure oxygen.37. The de-burring method of claim 24 wherein the auxiliary oxidizinggas comprises substantially pure oxygen.
 38. The de-burring method ofclaim 24 wherein the auxiliary oxidizing gas comprises air.